Methods and apparatus for operating air conditioning systems with an economizer cycle

ABSTRACT

Methods and apparatus are provided for enhancing the performance of rooftop air conditioning systems by operating such systems with an economizer cycle and utilizing a blend incorporating R32 and R125 refrigerants as a working medium, wherein such benefits are related to at least the performance (e.g. capacity and/or the energy efficiency ratio) of the rooftop air conditioning system operating at various environments (e.g. temperatures at and above 95° F.).

FIELD OF THE INVENTION

This invention relates to air conditioning systems, and, in particular,to methods and apparatus for operating packaged air conditioning systems(e.g. rooftop air conditioning systems) with an economizer cycle so asto achieve measurable performance-related benefits.

BACKGROUND OF THE INVENTION

It is known in the refrigeration art that various benefits (e.g.,increased system capacity and/or efficiency) can be derived fromoperating a refrigeration system with a so-called “economizer cycle.” Itis also understood that these benefits are magnified when there is ahigh pressure ratio between compressor suction and discharge, such aswould occur when a high temperature differential exists during operationof a refrigeration system. For example, appreciable system benefits areachieved when operating a supermarket or transport refrigeration systemwith an economizer cycle in environments wherein the temperaturedifferential (between compressor saturated suction and saturateddischarge temperature) for the refrigerant circulated through the systemis typically about 130° F.

In contrast, pressure ratios are much lower for air conditioningsystems. This is because the temperature differential encountered duringoperation of air conditioning systems is markedly less than that whichis typically encountered in a refrigeration context. Consequently, thosein the air conditioning field have been discouraged from operating airconditioning systems with an economizer cycle, particularly since it istheir belief that doing so would add non-nominal costs and complexitiesto the systems that would not be recouped by performance-relatedbenefits and/or enhancements. Thus, those who manufacture, sell and/orutilize air conditioning systems have been unable, thus far, to reap thevarious benefits that perhaps could be realized through operation ofsuch air conditioning systems with an economizer cycle.

While that alone is problematic, it is made more difficult by the recentintroduction of various legislation and industry regulations, which havegreatly affected the air conditioning industry by defining minimumefficiency standards for air conditioning systems and by instituting agradual phase-out of (followed, over time, by a total ban on) certainthermodynamically suitable and efficient refrigerants that also happento contain hydrochlorofluorocarbons (HCFCs), e.g., R22 refrigerant.

The phase-out/ban on R22 is particularly significant to those in theart, since there is a concern that the performance of air conditioningsystems may be negatively impacted due to the resultant introduction ofalternate, “environmentally friendly” refrigerants that havethermo-physical properties considerably different than those of R22.Among the most widely utilized of these alternate refrigerants is theR410A refrigerant blend, which most in the art believe exhibitsperformance deficiencies under certain environmental conditions (e.g.,at high ambient temperatures) as compared to R22 refrigerant.

Thus, there is a need to develop air conditioning systems, methods andequipment that can be utilized within the scope of legislation andindustry regulations yet that still can provide measurableperformance-related benefits when operated with an economizer cycle.

SUMMARY OF THE INVENTION

These and other needs are met by the present invention, which providesmethods and apparatus for operating air conditioning systems with aneconomizer cycle, (or so-called “vapor injection cycle”). In particular,the present invention provides for operating a rooftop air conditioningsystem or unit with an economizer cycle under certain conditions (e.g.,in certain temperature ranges and/or using certain refrigerants) so asto achieve performance-related benefits with regard to at least thecapacity and/or the energy efficiency ratio of the air conditioningsystem as compared to an air conditioning system that is operatedutilizing a conventional (i.e., non-economized) cycle. These benefitsare especially important because they are achieved while complying withall applicable legislative and industrial regulations.

In accordance with an exemplary aspect of the present invention, suchbenefits occur when a rooftop air conditioning unit is operated with aneconomizer cycle using R410A or a similar blend as a refrigerant (i.e.,working medium), and/or wherein the rooftop system is operated in anoutdoor setting having an ambient temperature at or above the standardARI rating/point—for certain equipment—of 95° F.

In accordance with another exemplary aspect of the present invention inwhich R410A or a similar composition blend is utilized as therefrigerant for the rooftop air conditioning system, the blend can becomprised of about 47% to about 53% of R32 refrigerant and about 53% toabout 47% of R125 refrigerant.

In accordance with yet another exemplary aspect of the presentinvention, the refrigerant blend for the rooftop air conditioning systemcan further include other additives such as oils (e.g., polyolesteroils, polyvinylether oils, mineral oils, Alkyl Benzene oils, andcombinations of one or more of these and/or other oils) and/orlubrication enhancement additives, wherein small amounts of theadditive(s) are circulated within the air conditioning system along withthe refrigerant blend.

Still other aspects, embodiments and advantages of the present inventionare discussed in detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

For a fuller understanding of the nature and desired objects of thepresent invention, reference is made to the following detaileddescription taken in conjunction with the accompanying figures, whereinlike reference characters denote corresponding parts throughout theviews, and in which:

FIG. 1 is a schematic view of an economizer cycle for an airconditioning system;

FIG. 2 is a schematic view of an alternative economizer cycle for an airconditioning system;

FIG. 3 is a graph depicting the absolute pressure versus specificenthalpy (i.e., a P-h diagram) for the economizer cycles of FIGS. 1 and2;

FIG. 4 is a graph depicting the comparatively beneficial resultsrelating to capacity that were obtained when operating a rooftop airconditioning system with an economizer cycle using an R410A refrigerant;and

FIG. 5 is a graph depicting the comparatively beneficial resultsrelating to energy efficiency ratio that were obtained when operating arooftop air conditioning system with an economizer cycle using an R410Arefrigerant.

DETAILED DESCRIPTION

The present invention provides methods and apparatus for operating arooftop air conditioning system with an economizer cycle. As notedabove, those in the air conditioning field had largely written off thepossibility of operating an air conditioning system with an economizercycle within the confines of legislation and industrial regulations yetso as to receive performance-related benefits that would not be morethan offset by the added costs and complexities of running the system.However, in accordance with the present invention it was unexpectedlydiscovered that operating packaged air conditioning systems (e.g.,rooftop air conditioning systems) with an economizer cycle under certainoperation conditions (e.g., in certain temperature ranges and/or usingcertain refrigerants) results in measurable performance-related benefitswhile complying with applicable legislative and/or industrialregulations.

An exemplary economizer vapor injection cycle 100 for an airconditioning system is depicted in FIG. 1. In accordance with theeconomizer vapor injection cycle (“economizer cycle”) 100, a compressor10 delivers high pressure refrigerant to a discharge line 20 and then toa condenser 30. The refrigerant exits the condenser through a liquidline and is split between a main flow line 40 and an auxiliary flow line50. Although the percentages of refrigerant that are routed to the mainflow line 40 and to the auxiliary flow line 50 can vary, it is currentlypreferred that between about 8% and about 12% by weight of the totalrefrigerant flow be fed to the auxiliary flow line 50, wherein thebalance of the refrigerant is routed to the main flow line 40.

From the main flow line 40, refrigerant is fed through an economizerheat exchanger 95 to a main expansion device 60, then to an evaporator70, and finally back to the compressor 10. From the auxiliary flow line50, auxiliary refrigerant flow is fed to the economizer expansion device90 (which reduces the pressure and temperature of the auxiliaryrefrigerant as compared to the pressure and temperature of therefrigerant in the main flow line 40) and to the economizer heatexchanger 95 in a predetermined manner, preferably in a counter-flowconfiguration with respect to the main refrigerant flow. The auxiliaryrefrigerant flow is then fed back to the compressor 10 at anintermediate (i.e., between suction and discharge) pressure. A bypassvalve 80 is present to allow a portion of partially compressedrefrigerant to flow back to compressor suction (e.g., in aconventional/non-economized mode of operation) should there be a desireto unload the compressor.

The temperature difference between the main refrigerant and theauxiliary refrigerant can vary, and is dependent on system design andoperating conditions; however, according to a currently preferredembodiment of the present invention, the auxiliary refrigerant will havea temperature of about 25° F. to about 40° F. less than that of the mainrefrigerant, wherein about 15° F. to about 35° F. of the extratemperature reduction is obtained due to heat transfer interactionbetween the main and auxiliary refrigerant flows in the economizer heatexchanger 95.

Thus, the economizer cycle 100 is beneficial because it causes a certainpercentage (e.g., about 88% to about 92%) of refrigerant to be furthersubcooled (e.g., by about 15° F. to about 35° F.) to a temperature lowerthan the temperature that would be achieved if the air conditioningsystem of FIG. 1 were to be operated in a conventional (i.e.,non-economized) cycle. As a result, the refrigerant will have a greatercooling potential while reaching evaporator 70.

FIG. 2 depicts an air conditioning system that operates with analternate economizer cycle 100A. The FIG. 2 economizer cycle 100A isidentical to the FIG. 1 cycle 100, with the exception that the auxiliaryflow in the FIG. 2 cycle is originated downstream of the economizer heatexchanger 95, rather than upstream as it is in the FIG. 1 cycle.

FIG. 3 is a P-h diagram for the economizer cycle 100 of FIG. 1 and theeconomizer cycle 100A of FIG. 2, wherein the points 1, 2, 3, 4, 5, 6, 7,7′ and 7 in the FIG. 3 diagram correspond to those same labeled pointswithin the economizer cycles of FIGS. 1 and 2.

Still further alternate embodiments of the economizer cycles 100, 100Aof FIGS. 1 and 2 are within the scope of the present invention,including but not limited to those described in the U.S. Pat. No.6,658,867 to Taras et al., the entirety of which is incorporated byreference herein. For example, either or both of the economizer cycles100, 100A of FIGS. 1 and 2 can be modified to incorporate a tandemcompressor arrangement, wherein at least two compressors 10 are arrangedand operated in parallel in which one or more of the at least twocompressors can be selectively started and stopped to provide part-loadoperation for the refrigerant systems depicted in FIGS. 1 and 2.Additionally, multi-circuit systems (i.e., systems with multipleindependent circuits, as are known in the art) can benefit from thepresent invention. In such systems, multiple circuits can be operated toprovide similar part-load capability, such as in the case of the tandemcompressors, which are known in the art.

It has been unexpectedly discovered in accordance with the presentinvention that utilizing either of the economizer cycles 100, 100A ofFIGS. 1 and 2 or any of those described in the '867 patent to Taras etal. in certain contexts can provide highly beneficial results withregard to air conditioning system performance, especially with regard tothe capacity and the energy efficiency ratio (EER) of a rooftop airconditioning system. For purposes of the present invention a “rooftopair conditioning system” refers to a packaged air conditioning system(in contrast to what is referred to in the art as a “split airconditioning system”) that is sited above ground, e.g., on top of abuilding or structure. Also, for purposes of the present invention, an“economizer cycle” refers to the economizer cycle 100 of FIG. 1, theeconomizer cycle 100A of FIG. 2, one of the economizer cycles depictedand/or described in the '867 patent to Taras et al., or any other knowneconomizer cycles.

For example, as shown in the data reflected in FIGS. 4 and 5, it wasdiscovered through experimentation and modeling that utilizing R410A asa refrigerant with an economizer cycle for a rooftop air conditioningsystem provides certain performance-related benefits as compared tousage of R410A in a rooftop system employing a conventional (i.e.,non-economized) cycle. FIG. 4 depicts a graph of the relative capacity(with respect to the R22 conventional cycle) versus ambient temperatureresults of modeling and experimental validation for a rooftop airconditioning system that was operated (a) with an economizer cycle usingR410A as a refrigerant in accordance with the present invention(described on the graph as “R410A Economized”), and (b) with aconventional cycle using R410A as a refrigerant (described on the graphas “R410A Conventional”). Similarly, FIG. 5 depicts a graph of energyefficiency ratio (EER) versus ambient temperature results of modelingand experimental validation for a rooftop air conditioning system thatwas operated (a) with an economizer cycle using R410A as a refrigerantin accordance with the present invention (described on the graph as“R410A Economized”), and (b) with a conventional (i.e., non-economized)cycle using R410A as a refrigerant (described on the graph as “R410AConventional”).

It should be noted that for the experiments reflected in both FIGS. 4and 5, the equipment utilized to perform the “R410A Economized” and“R410 Conventional” testing typically was not identical, since theconventional system would include larger heat exchangers than theeconomizer system, in order to obtain performance parity at the ARIconditions of 80° F./67° F. indoor dry bulb/wet bulb temperatures and95° F. ambient temperature. Upsizing heat exchangers is a typicalmeasure taken by those in the art in an attempt to improve theperformance (i.e., capacity and/or energy efficiency ratio) of an airconditioning system.

As shown in FIGS. 4 and 5, the capacity and the energy efficiency ratioof both the conventional system and the economizer system aresubstantially equal at the standard ARI rating/design point. Theseresults indicate the benefits of the economizer system of the presentinvention, since it was able to achieve capacity and an energyefficiency ratio values comparable to those observed with respect to theconventional system at the standard ARI rating/design point of 80°F./67° F. indoor and 95° F. ambient temperatures despite typically notbeing equipped with larger heat exchangers. As used herein, the phrase“ambient temperature” refers to the outdoor temperature where a rooftopair conditioning system is sited, wherein such temperature can be (andtypically is) effectively higher than the temperature reading that wouldbe registered on a thermometer, e.g., due to a direct sunlight. Also,saturated discharge temperatures corresponding to specific ambienttemperatures could be higher than expected due to the natural aging ofthe air conditioning equipment.

The results in FIGS. 4 and 5 also indicate that the benefits of theeconomizer system of the present invention become even more pronounced(versus the conventional system) as the systems are operated at ambienttemperatures above the ARI rating/design point of 95° F. For example,the data reflected in FIG. 4 indicates that the capacity of a rooftopair conditioning system operated with a conventional cycle using R410Aas a refrigerant begins to show a noticeable degradation (i.e.,decrease) at temperatures above 95° F. despite being equipped withlarger heat exchangers. Specifically, as shown in FIG. 4, the capacitydegradation of the conventional system is already 9% (in comparison toan R22 system not equipped with enlarged heat exchangers) at 125° F.ambient temperature. In contrast, and as also shown in FIG. 4, when therooftop air conditioning system was operated in accordance with thepresent invention with an economizer cycle using the same R410A blend asthe refrigerant, the system exhibited a much less precipitous capacitydegradation, e.g., only 5% at 125° F. ambient temperature.

Similarly beneficial results with respect to the energy efficiency ratio(EER) are demonstrated with reference to FIG. 5—that is, there was ameasurable benefit achieved though use of refrigerant blends such asR410A with an economizer cycle for a rooftop air conditioning systemabove 95° F. in accordance with the present invention. Specifically, arooftop air conditioning system operated with a conventional cycle usingR410A as a refrigerant exhibits an energy efficiency ratio degradation(i.e., decrease) of 12% (once again, in comparison to an R22 system notequipped with enlarged heat exchangers) at 125° F. ambient outdoortemperature, despite of being equipped with larger heat exchangers,whereas a rooftop air conditioning system exhibits only a 5% energyefficiency ratio degradation at 125° F. outdoor ambient temperature whenoperated with an economizer cycle and utilizing R410A as the refrigerantin accordance with the present invention.

The comparative capacity and energy efficiency benefits shown in FIGS. 4and 5 for the present invention are particularly significant becausethey occurred for ambient temperatures at and especially above 95°,which are routinely encountered at the top of a structure or building(e.g., a roof) during the daytime in certain hot, dry, populatedclimates (e.g., Nevada, Arizona, The Middle East), and which is wheresuch benefits are most needed because an air conditioning systems arerelied upon at such high temperatures to deliver as much cooling aspossible.

Moreover, the fact that these beneficial results occurred with respectto a rooftop air conditioning system is also very important. In standard(i.e., “split” or residential) air conditioning systems, certainportions of the system (e.g., the condensing unit) are typicallyinstalled on the side of a structure, not atop the structure as they arefor a rooftop system. Thus, rooftop air conditioning systems are exposedto significant additional heat loads not present in other (e.g., “split”or residential) air conditioning applications because the hot ambientair that blows over the evaporator and condenser coils is additionallypreheated by hot rooftop surfaces exposed to direct sunlight, which alsoacts to provide extra radiant heat load by directly or indirectly (e.g.,through conduction and convection) heating various components of therefrigerant system. Further, due to the location and conditions underwhich they are operated, rooftop air conditioning systems are vulnerableto edging and/or infrequent maintenance, both of which can cause theeffective operation temperature of the system to be higher than usual.

Thus, it is very significant that air conditioning systems of thepresent invention can be operated with an economizer cycle under thedemanding conditions of rooftop air conditioning systems and withenvironmentally friendly refrigerant blends such as R410A yet stillexhibit comparatively less capacity and energy efficiency degradationthan air conditioning systems that are operated with a conventionalcycle and that are equipped with a larger heat exchanger.

In summary, significant capacity benefits (e.g., a lower capacitydegradation) and energy efficiency benefits (e.g., a lower energyefficiency ratio degradation) are achieved when a rooftop airconditioning system is operated with an economizer cycle using R410Arefrigerant as compared to the same system being operated with aconventional cycle and/or for standard (i.e., “split” or residential)air conditioning applications. Moreover, these benefits are especiallypronounced when the system is operated under conditions wherein theambient outdoor temperature is above 95° F., in the range of about 95°F. to 125° F., or above 125° F., and when extrapolated over the usablelifetime of the rooftop air conditioning system.

It should be noted that although R410A is generally a blend of 50% byweight of R32 refrigerant and 50% by weight of R125 refrigerant, anyreferences to “R410A” herein should be interpreted to refer to a blendof between about 47% and about 53% (both inclusive) by weight of R32 andbetween about 53% and about 47% (both inclusive) by weight percentage ofR125. Moreover, these ranges can be adjusted in accordance with thepresent invention, and/or some amounts of other refrigerants (e.g.,R134a) can be added to the blend. In an embodiment wherein RI 34 a isadded, it is currently preferred to add no more than 5% by weightthereof.

Further, one or more additives can be included in the R410A-likerefrigerant blend in accordance with the present invention. Exemplarysuch additives include, but are not limited to oils (e.g., polyolester(POE) oils polyvinylether (PVE) oils, Alkyl Benzene oils, mineral oils,or a mixture or combination of one or more of these oils, wherein theviscosity grades of such oils can vary but are generally in the range ofabout 20 to about 70 centistokes and when the oil viscosity is measuredwithout the refrigerant at temperature of 100 F.) and/or one or morelubrication enhancement additives known in the art. The additives can beadded to the refrigerant blend as is generally known in the art, e.g.,by being circulated within the air conditioning system along with therefrigerant.

Although the present invention has been described herein with referenceto details of currently preferred embodiments, it is not intended thatsuch details be regarded as limiting the scope of the invention, exceptas and to the extent that they are included in the following claims—thatis, the foregoing description of the present invention is merelyillustrative, and it should be understood that variations andmodifications can be effected without departing from the scope or spiritof the invention as set forth in the following claims. Moreover, anydocument(s) mentioned herein are incorporated by reference in theirentirety, as are any other documents that are referenced within thedocument(s) mentioned herein.

1. An air conditioning system, comprising: a rooftop air conditioningunit operated with an economizer cycle, wherein the rooftop airconditioning unit utilizes at least one predetermined refrigerant as aworking medium.
 2. The air conditioning system of claim 1, wherein theat least one predetermined refrigerant is a blend of R32 refrigerant andR125 refrigerant.
 3. The air conditioning system of claim 2, wherein theat least one predetermined refrigerant is a blend of about 47% to about53% by weight of R32 refrigerant and about 53% to about 47% by weight ofR125 refrigerant.
 4. The air conditioning system of claim 1, wherein theat least one predetermined refrigerant includes at least one additive.5. The air conditioning system of claim 4, wherein each of the at leastone additive is an oil.
 6. The air conditioning system of claim 5,wherein each of the at least one oil has a viscosity grade between about20 and about 70 centistokes.
 7. The air conditioning system of claim 5,wherein each of the at least one oil is selected from the groupconsisting of polyolester oil, polyvinylether oil, Alkyl Benzene oil,mineral oil, and a mixture of two or more thereof.
 8. The airconditioning system of claim 4, wherein the at least one additive is anadditional refrigerant.
 9. The air conditioning system of claim 8,wherein the additional refrigerant is R134a.
 10. The air conditioningsystem of claim 9, wherein the amount of R134a added to the system is upto and including 5% by weight.
 11. The air conditioning system of claim4, wherein the at least one additive is a lubrication enhancementadditive.
 12. A rooftop air conditioning system which is operated withan economizer cycle and which uses a working medium comprised of a mixedrefrigerant of R32 and R125.
 13. The rooftop air conditioning system ofclaim 12, wherein the working medium is comprised of 47% to about 53% byweight of R32 refrigerant and about 53% to about 47% by weight of R125refrigerant.
 14. The rooftop air conditioning system of claim 12,wherein the working medium includes at least one additive.
 15. Therooftop air conditioning system of claim 14, wherein each of the atleast one additive is an oil.
 16. The rooftop air conditioning system ofclaim 15, wherein each of the at least one oil has a viscosity gradebetween about 20 and about 70 centistokes.
 17. The air conditioningsystem of claim 15, wherein each of the at least one oil is selectedfrom the group consisting of polyolester oil, polyvinylether oil, AlkylBenzene oil, mineral oil, and a mixture of two or more thereof.
 18. Theair conditioning system of claim 14, wherein the at least one additiveis an additional refrigerant.
 19. The air conditioning system of claim18, wherein the additional refrigerant is R134a.
 20. The airconditioning system of claim 19, wherein the amount of R134a added tothe system is up to and including 5% by weight.
 21. The air conditioningsystem of claim 14, wherein the at least one additive is a lubricationenhancement additive.
 22. A method of improving the performance of arooftop air conditioning system, comprising the steps of: providing arooftop air conditioning system; and operating the rooftop airconditioning system with an economizer cycle.
 23. The method of claim22, further comprising the step of: utilizing a mixture of R32 and R125refrigerants as a working medium for the system.
 24. The method of claim23, wherein the working medium includes at least one additive.
 25. Themethod of claim 24, wherein each of the at least one additive is an oil.26. The method of claim 25, wherein each of the at least one oil has aviscosity grade between about 20 and about 70 centistokes.
 27. Themethod of claim 25, wherein each of the at least one oil is selectedfrom the group consisting of polyolester oil, polyvinylether oil, AlkylBenzene oil, mineral oil, and a mixture of two or more thereof.
 28. Theair conditioning system of claim 24, wherein the at least one additiveis an additional refrigerant.
 29. The air conditioning system of claim28, wherein the additional refrigerant is R134a.
 30. The airconditioning system of claim 29, wherein the amount of R134a added tothe system is up to and including 5% by weight.
 31. The air conditioningsystem of claim 24, wherein the at least one additive is a lubricationenhancement additive.
 32. The method of claim 22, wherein the step ofoperating the rooftop air conditioning system is performed in an outdoorambient temperature above 95° F.
 33. The method of claim 22, wherein thestep of operating the rooftop air conditioning system is performed in anoutdoor ambient temperature between about 95° F. and about 125°.
 34. Arooftop air conditioning system, comprising: a compressor; a condenserin communication with the compressor via at least a first refrigerantline; a first expansion device in communication with the condenser viaat least a second refrigerant line; an evaporator in communication withthe first expansion device via at least a third refrigerant line and incommunication with the compressor via at least a fourth refrigerantline, a second expansion device in communication with the condenser viaat least a fifth refrigerant line; and a heat exchanger in communicationwith the second expansion device via at least a sixth refrigerant lineand in communication with the compressor via at least a seventhrefrigerant line; wherein the rooftop air conditioning system isoperated with an economizer cycle and utilizes at least onepredetermined refrigerant as a working medium.
 35. The rooftop airconditioning system of claim 34, wherein the system comprises at leasttwo compressors.
 36. The rooftop air conditioning system of claim 35,wherein at least two compressors are tandem compressors.
 37. The rooftopair conditioning system of claim 34, wherein the system is amulti-circuit system.
 38. The air conditioning system of claim 34,wherein the at least one predetermined refrigerant is a blend of R32refrigerant and R125 refrigerant.
 39. The air conditioning system ofclaim 38, wherein the at least one predetermined refrigerant is a blendof about 47% to about 53% by weight of R32 refrigerant and about 53% toabout 47% by weight of R125 refrigerant.
 40. The air conditioning systemof claim 34, wherein the at least one predetermined refrigerant includesat least one additive.
 41. The air conditioning system of claim 40,wherein each of the at least one additive is an oil.
 42. The airconditioning system of claim 41, wherein each of the at least one oilhas a viscosity grade between about 20 and about 70 centistokes.
 43. Theair conditioning system of claim 41, wherein each of the at least oneoil is selected from the group consisting of polyolester oil,polyvinylether oil, Alkyl Benzene oil, mineral oil, and a mixture of twoor more thereof.
 44. The air conditioning system of claim 40, whereinthe at least one additive is an additional refrigerant.
 45. The airconditioning system of claim 44, wherein the additional refrigerant isR134a.
 46. The air conditioning system of claim 45, wherein the amountof R134a added to the system is up to and including 5% by weight. 47.The air conditioning system of claim 40, wherein the at least oneadditive is a lubrication enhancement additive.